This invention relates generally to the art of centrifugal pumps and more particularly to the assembly of sealless pumps.
U.S. Pat. No. 4,871,301, issued Oct. 3, 1989, titled "Centrifugal Pump Bearing Arrangement", invented by me, relates to a sealless pump of the type having an internal rotor carrying a series of permanent magnets which are magnetically coupled with an external rotor carrying a second series of permanent magnets and driven by a driver such as a electric motor. The magnetic coupling eliminates shaft seals which have the risk of leaking; therefore, the pumped fluid can be contained in an envelope which does not contain openings for a rotor shaft or the like which are subject to leaking. As pumps of this type are made larger, the magnetic forces of the magnets become larger and in some cases large enough to cause great difficulty in assembling the magnetically coupled rotor devices without injury occurring to either the pump or to workmen assembling the pump. For example, in pumps of approximately 50 horsepower the axial forces on the magnetic rotors can be as large as 200 pounds.
The assembly of the outer or driving magnet rotor must be carried out with the rotor located centrally on the containment shell enclosing the inner magnet rotor and with a controlled axial movement of the outer magnet rotor into position over the inner magnet rotor. If the outer magnet rotor moves out of a central position, or moves axially in an uncontrolled manner, tremendous forces can pull it into abutment with other portions of the pump causing injury to either or both the pump and the workmen carrying out the assembly of the pump. This same problem exists in the field during disassembly or reassembly of the pump during a maintenance or repair procedure.